Different transmission throughputs or baud rates have been proposed for Rate Adaptive Digital Subscriber Line (RADSL). K. Sistanizadeh, J. Waldhuter, H. Suyderhoud, and M. Sorbara, Recommendation on Symbol Rates, Constellations, and Spectral Placement and Shaping for the CAP/QAM Spec., Joint T1E1 CAP/QAM RADSL Ad Hoc Group Contribution, T1E1/97-134, Mar. 5, 1997; H. Samueli, R. Joshi, M. Darveau, and R. Carsten, Draft PMD Specification for Rate-Adaptive ADSL (RADSL), Broadcom T1E1 CAP/QAM RADSL Ad Hoc Group Contribution, T1E1/97-013, Jan. 22-23, 1997. H. Samueli, R. Joshi, M. Darveau, and R. Carsten, Draft PMD Specification for Rate-adaptive ADSL (RADSL), Broadcom T1E1 CAP/QAM RADSL Ad Hoc Group Contribution, T1E1/97-013, Jan. 22-23, 1997. There was a concern that the currently proposed throughput step size was too big. R. A. McDonald, "Transceiver Rate Adaptation Step Sizes," Pacific Bell Telesis Technologies Laboratory T1E1 CAP/QAM RADSL Ad Hoc Group Contribution, T1E1/97-019, Jan. 22-23, 1997.
The relationship between baud rates and a fixed system clock is first explored.
Baud Rates Derived from A Fixed Master Clock
Baud rates .function..sub.B.sub..sub.i are usually derived from a fixed common clock frequency .function..sub.clock according to EQU .function..sub.B.sub..sub.i =.function..sub.clock /m.sub.i
where m is an integer. A shift register of n bits, where Max(m.sub.i)&lt;2.sup.n, is necessary to derive the baud rate from the master clock.
For the proposed baud rates from Globspan Table 1, we have .function..sub.clock =114.24 MHz, m.sub.1 =840, m.sub.2 =336, m.sub.3 =168, m.sub.4 =140, m.sub.5 =120, m.sub.6 =105. K. Sistanizadeh, J. Waldhuter, H. Suyderhoud, and M. Sorbara, Recommendation on Symbol Rates, Constellations, and Spectral Placement and Shaping for the CAP/QAM Spec., Joint T1E1 CAP/QAM RADSL Ad Hoc Group Contribution, T1E1/97-134, Mar. 5, 1997.
TABLE 1 Proposed Baud Rates from GlobSpan Up Downstream Baud Rate 136 340 680 816 952 1088
For the proposed baud rates from Broadcom
In Table 2, we have .function..sub.clock =2.016 MHz, m.sub.1 =24, m.sub.2 =16, m.sub.3 =8, m.sub.4 =4, m.sub.5 =3, m.sub.6 =2. H. Samueli, R. Joshi, M. Darveau, and R. Carsten, Draft PMD Specification for Rate-Adaptive ADSL (RADSL), Broadcom T1E1 CAP/QAM RADSL Ad Hoc Group Contribution, T1E1/97-013, Jan. 22-23, 1997
TABLE 2 Proposed Baud Rates from Broadcom Up Downstream Baud Rate 84 126 252 504 672 1008